Thermostatically controlled electric soldering iron

ABSTRACT

An electrically heated soldering iron includes a tubular body of two rigidly connected colinear parts, a bit and heater element at the front end of said body and a hollow handle at the rear end of said body. A thermostatic control is disposed within the body and includes a wire having a low coefficient of thermal expansion secured at its front end to a rear part of the bit and secured at its rear end to operating means for a switch in the handle. At least a part of the rear end of the bit is of a higher coefficient of thermal expansion than the effective coefficient of thermal expansion of said wire, and said wire is tensioned as the bit heats up to operate said switch means.

2,475,376 7/1949 Darling United States Patent Robert A. Adamson 35 Courtfield Rise, West Wickham, Kent; Colin P. Adamson, Monorest Westerham Road, Biggin Hill, Kent, England [21] Appl. No. 783,554

[22] Filed Dec. 13,1968

[45] Patented Feb. 23, 1971 [72] Inventors [54] THERMOSTATICALLY CONTROLLED ELECTRIC SOLDERING IRON 1 Claim, 3 Drawing Figs.

[5 6] References Cited UNITED STATES PATENTS Primary ExaminerA. Bartis Attorneys-Emory L. Groff and Emory L. Groff, .I r.

ABSTRACT: An electrically heated soldering iron includes a tubular body of two rigidly connected colinear parts, a bit and heater element at the front end of said body and a 110110 handle at the rear end of said body. A thermostatic control is disposed within the body and includes a wire having a low coefficient of thermal expansion secured at its front end to a rear part of the bit and secured at its rear end to operating means for a switch in the handle. At least a part of the rear end of the bit is of a higher coefficient of thermal expansion than the effective coefficient of thermal expansion of said wire, and said wire is tensioned as the bit heats up to operate said switch means.

falls below a certain .temperature. Thus the frrrERMosrA'rrcALLY CONTROLLED ELECTRIC somanrucmon 1 it BACKGROUND or INVENTION This invention concerns electrically heated soldering irons.

7 forms a colinear front part of a tubular The main object of the invention is to provide-la construction trolled.

Another object of the'invention is to provide a thermostatic control which is of a simple construction, and which can be incorporated in irons of small size. A further object is to provide 'an iron in which the control can be fitted easilyor removed easily for repair. Yet another object of the invention is to provide a thermostatic control in which the operating temperature can be adjusted easily without dismantling'the iron.

SUMMARY OF'INVENTIONI' According to the invention the: ironcomprises a tubular body, a bit and heater element at the front end of said body, a hollow handle at the rear end of said body, a thermostatic control within the body, said control comprising a wire within said body and secured at its front endto a rear part of the bit,

rear end of the said wire is secured, atleast a part at the rear end of said bit of a higher coeffrcient'ofthermal expansion than the effective coefficient of thermal expansion of said wire, said wire being tensioned asthebit heats up to operate or like low expansion material. The rod or wire alsopreferably is of lnvarsteeL'but again,

only a front part of the rod or wire need be 'of this material." I 1 Thetube may constitute the main body or it may bewithin an outer casing, for example of close wound iron wire. I

' 'It will be appreciatedthat withthe construction according to the invention, the switch is operated to interrupt the current I body 14a within the casing 10, this tube being of Invar steel.

A wire 15 of low expansion metal such as Invar steel is within the body comprising the tube parts 12a and 14a, and is securedby means of a nut 17a at the front end. The rear end of the tube 14a is secured in a bust or boss 19 and a bell crank lever23 is mounted on .a support secured to the bush by its pivot and within the handle 11, to one leg of which the rear end of the wire 15 is secured. The other leg of the bell crank operates a microswitch 25. The angular setting of the bell crank can be adjusted by means of ascrew 26, through a hole 26a through the handle 11. A line cord C is anchored in thehandle by a grip screw 27, the leads being connected to pins operating means fora switch in the handle to which means the A mounted on the bush. The support bracket 20 is used for the mounting of the assembly including the body, so that by removing the screws 29, thecomplete assembly can be removed from the handle.

With the above construction, when the iron is cold the switch contacts make. As the iron heats up, owing to the differential expansion of the steel wire and front tube part 12a, the wire is tensioned untilat the predetermined temperature the bell crank is moved sufficiently to press on the operating member of the switch 25 and open the switch contacts.

A neon indicator lamp N is connected through a suitable resistance in the circuit, so as to be energized when the heater element is energized. The handle 1 I can be of a transparent or translucent synthetic plastics material.

In the embodiment illustrated in FIG. 3, the rod or wire 15 is within a brass or copper tube 14 which extends at its front end into a blind bore 12b in the bit, the wire end andtube end in this bore being secured together at 17. The tube 14 is within -an outer tube 18 which is within thecasing 10, and the tube 14 is secured by a nut 21 to the bush 19. I

In this embodiment only a front part 15a of the rod or wire is of Invar steel. This construction could also be used in the embodiment of FIGS. 1 and 2.

The iron herein can be constructed easily and cheaply, and can be fitted into a tubular handle of small cross sectional area. The on/off switching action is rapid with little time lag from actual bit te'mperature,as the part 12a, FIGS. land 2, or the front part of the tube 14, FIG. 3, is adjacent the heating element. Adjustment of the I possible without any dismantling of the iron.

1, An electrically heated soldering iron comprising a tubular body of two rigidly connected colinear parts; a bit and "an electrical heater element for said bit carried by a front one of said to the element by tensioning of the rod or wire. This enables a thin rod or wire to be used sothat irons of small size incorporating the thermostat control can be constructed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 3 is a view similar to FIG. 1 of the second embodiment.

Like numerals refer to like parts in all of the views.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring firstly to FIGS. 1 and 2, the iron has a wire wound outer body casing 10, handle 11, and a bit tip 12.- The bit inhaving a lower coefficient cludes a rear hollow part 124 on to which the tip 12 engages, j

for example by screwthreads, which part 12a is mainly within the casing 10 and forms a part of the body, and a heating element (not shown) is wound (with suitable insulation) around the saidpart 12a.

The part 120 is of high expansion'metal such as copper and two colinear parts; a bush rigidly secured about a rear one of said two colinear parts; a hollow handle having an open end in which said bush is telescopically received, said handle rigidly secured to said bush to extend away from said rear one of said two colinear parts; a support member directly carried by said bush and positioned within said hollow handle; an electrical switch mounted on said support memberand arranged to make and break the electrical supply to said heater element;

. an operating member pivotally mounted on said support member and arranged to operate said. electrical switch; and a thermostatic controlcomprising a tensioned wire passing through said tubular body and being rigidly secured at its front end to said front one of said two colinear parts and rigidly secured at its rear end to said operating member, said wire of thermal expansion than at least said front one of said two colinear parts, whereby on heating of said heater element to a predetermined temperature, said wire is tensioned such as to cause said operating member to operate said electrical switch to break the electrical supply to said heater element, and on cooling of said heater element to below said predetermined temperature said wire is slackened sufficiently to releasesaid operating member from said electrical switch to allow said electrical switch to remake the electrical supply to said heater element.

operating temperature also is 

